Resin-based composite materials, such as fiber-reinforced resins, are widely used for structural members of airplanes, automobiles, ships and the like for their light weight and high strength.
The resin-based composite materials are generally formed by stacking a plurality of prepregs which are made of fiber-reinforced resins and performing heating and pressurizing treatment thereon in an autoclave or the like.
For example, when the resin-based composite material is applied to rotor spars of a helicopter, the resin-based composite material is required to have sufficient strength to support a tensile load, which is generated by centrifugal force, and a rigid precision so that rotating blades can meet a designed natural frequency (dynamic behavior). It is known that the rigidity is proportional to the cube of board thickness of a member which is made of a resin-based composite material. Accordingly, in order to realize the rotor spars made of resin-based composite materials, it is necessary to minimize variations in board thickness with respect to a designed value (e.g., ±2% or less).
However, the resin-based composite material cured in an autoclave may possibly have a variation in board thickness larger than the above-stated desired variation value due to such causes as variations in board thickness of a prepreg itself, variations in resin fluidity during heating and a loss of the resin related thereto, variations in stacking process, and presence of air space remaining between layers. Accordingly, there is a need for a fabrication method capable of strictly controlling the board thickness of the resin-based composite material.
Patent Literature 1 discloses a method for fabricating a composite material by laying up (stacking) a plurality of prepreg plies in sequence on a molding surface of a base-mold member. In Patent Literature 1, the composite material is fabricated by repeating: a step of laying up a predetermined number of prepregs; a step of performing autoclave compression on the prepregs at about room temperature; and a step of laying up an auxiliary ply pack on an autoclaved layered product to adjust fluctuations in board thickness.